The purpose of this competing renewal application is to examine pathways to high school completion in a sample of 6000 students who are currently being followed across the three years of middle school. The large sample is very ethnically diverse: about 30% Latino, 20% White, with the remaining 50% approximately evenly divided between African American, Asian/Pacific Islander, and youth who identify as multiethnic. The sample was recruited in three cohorts from 26 middle schools in southern and northern California that systematically varied in ethnic diversity. Longitudinal data from 6th-8th grade are being gathered on students' social and academic adjustment to test hypotheses about the psychosocial benefits and challenges of ethnic diversity in urban middle schools. It is anticipated that the students will transition to close to 100 high schools that also vary in ethnic diversity. Using the rich middle school data as a starting point, this application will examine the high school transition and pathways to high school completion as a developmental process. Data assessing constructs studied during middle school and new constructs more unique to the high school years will be gathered on the same students from 9th-12th grade and one year beyond. The high school pathways phase of the research has three specific aims. Aim 1 examines how middle school social and academic history predicts the degree to which the critical 9th grade transition is smooth versus disruptive. Aim 2 examines pathways, or mediating mechanisms, to high school completion focusing on three developmental competencies: academic achievement, mental health, and civic engagement. Novel hypotheses are tested about the ways in which school ethnic diversity shapes each developmental pathway. Aim 3 examines individual risk factors, such as obesity and sexual orientation, and systemic school risk factors, such as harsh discipline, that can disrupt successful pathways. By capitalizing on an existing longitudinal sample, the long-term goal of this research is provide new insight into the challenges that adolescents of color face as they navigate urban middle schools and high schools that vary in ethnic diversity as well as the mechanisms that promote strong academic preparation, mental health, and civic engagement in all youth on the brink of young adulthood. The focus on ethnic diversity across middle and high school is especially timely in a society where changing demographics are redefining the meaning of successful adaptation during the critical adolescent years.